Spinal stenosis, or narrowing of the spinal canal, affects millions of people, leading to disabling back and leg pain due to compression of the spinal nerves. Patients with severe spinal stenosis often require major surgery involving a spinal laminectomy, wherein portions of the lamina, spinous process and facet joints are removed to reduce the compression of the spinal nerves. Although spinal laminectomy can successfully relieve pressure from the spinal nerves, it requires a major surgery and may lead to a variety of complications including spinal instability, excessive blood loss, medical complications, recurrent stenosis and nerve scarring. These potential problems reduce the desirability of spinal laminectomy and make this operation unsuitable for some elderly patients with significant, pre-existing medical problems.
Correction of spinal stenosis through lengthening of the spinal pedicles has recently been described (U.S. Pat. Nos. 8,157,847, 7,166,107 and 6,358,254) and involves a novel surgical procedure of cutting and lengthening the spinal pedicles using an implanted medical device which is able to enlarge the spinal canal and alleviate the symptoms of spinal stenosis. Pedicle lengthening is much less invasive compared to spinal laminectomy and is capable of achieving a permanent expansion of the spinal canal. However, because the anatomy of the spinal pedicles varies throughout the lumbar spine and also between individuals, it would be desirable to have an implant capable of adapting to these anatomic variations. In particular, in situations where the vertebrae with a high convergence angle of the pedicle, such as is often seen at the L5 level, pedicle lengthening produces an offset or lateral shift between the upper and lower bone segment at the site of the pedicle osteotomy (bone cut).
For the foregoing reasons, there is a need for an improved device to accommodate the variations that may be encountered in pedicle anatomy and to allow offset between the upper and lower bone segments at the site of the pedicle osteotomy.